1. Field of the Invention
The present invention relates to a bonding apparatus, and more particularly relates to a bonding apparatus equipped with a moving mechanism which moves the bonding part that performs bonding work to arbitrary positions.
2. Prior Art
In wire bonders or wire boding apparatus, a plurality of bonding pads disposed on a die such as a semiconductor chip, etc. are connected to bonding leads on a circuit board, etc. with slender metal wires, etc. In order to perform bonding with a slender metal wire, etc. by way of correctly positioning the wire in specified positions of the bonding pads and bonding leads, a mechanism that moves the bonding head on which a bonding tool (through which the metal wire is passed and held) and positioning camera are mounted is required.
FIG. 15 shows, in a top view, the moving mechanism of a bonding head 20 in a conventional wire bonder 10.
In this mechanism, known as a so-called XY table mechanism as described in Japanese Patent Application Laid-Open (Kokai) No. 2002-329772, an X table 16 and a Y table 18 are both provided in a stacked fashion on a table holding stand 14 which is on a supporting stand 12 of the wire bonder 10, and the bonding head 20 is fastened to the Y table 18. A bonding tool 22, which has (on its tip end) a capillary that holds a metal wire passing through this capillary, and a position detection camera 24, are attached to the bonding head 20. A circuit board conveying path 50 is provided on the supporting stand 12, and circuit boards are conveyed thereon so that the circuit boards are positioned in a bonding work region 52 that is located more or less directly beneath the bonding tool 22.
The bonding head 20 is moved to arbitrary positions in the XY plane by moving the X table 16 in the X direction and moving the Y table 18 in the Y direction on this X table 16; then, the position detection camera 24 detects the position of the bonding head 20, and the bonding tool 22 is moved into the desired position based upon this position detection. Then, bonding work is performed by moving the bonding tool in the Z direction by means of a Z direction moving mechanism which is not shown in the drawings.
Here, the X table 16 is driven by an X direction linear motor 30, and it is moved in the X direction on the table holding stand 14 while being guided by a linear guide not shown in the drawings. More specifically, the X direction linear motor 30 includes a drive section 32 and a movable coil 34; and the drive section 32 generates a driving magnetic field in the direction perpendicular to the coil, and the movable coil 34 through which a coil current is caused to flow receives the X direction driving force from the driving magnetic field. The movable coil 34 is connected to the X table 16 via an arm 36.
The Y table 18 is driven by a Y direction linear motor 40, and can be moved in the Y direction on the X table 16 while being guided by a linear guide (not shown). The Y direction linear motor 40 includes a drive section 42 and a movable coil 44; and the drive section 42 generates a driving magnetic field in the direction perpendicular to the XY plane, and the movable coil 44 through which a coil current is caused to flow receives the Y direction driving force from the driving magnetic field as a result of the X direction component current. The movable coil 44 is connected to the Y table 18 via an arm 46.
By way of using the XY table mechanism as described above, the bonding head is moved to arbitrary positions and bonding work is performed. However, this mechanism has several problems.                1. Since the bonding head is mounted on an X table and Y table that are superimposed in two tiers, the mass that must be driven for movement is not the mass of the bonding head alone; and the masses of the X table and Y table are also added. Thus, a heavy mass must be driven, and it is difficult to have a high moving speed bonding head.        2. Since the Y table and bonding head are moved in the Y direction on the X table, an offset or positional discrepancy generates between the driving direction of the X direction driving motor and the position of the center of gravity of the Y table and bonding head. As a result, a rotational force is generated with respect to the bonding head by this X direction driving force; and in order to prevent this, it is necessary to increase the rigidity of the guide mechanism such as the linear guides, etc. As a result, the mass increases even further, and this hinders any increase in the moving speed of the bonding head.        3. There are limits to how far the precision of the straightness of the linear guides that determines the movement precision in the X direction and the movement precision in the Y direction can be improved; and thus, it is difficult to achieve a further improvement in the positioning precision.        4. When the X table is moved, the Y table on top of the X table is also moved. In other words, the movable coil of the Y direction actuator is moved not only in the Y direction but also moved in the X direction. Accordingly, the magnet that is used to generate the driving magnetic field of the Y direction actuator is required to be increased in size in order to cover the movement range of this movable coil, and the cost of the apparatus increases.        
In order to solve the problems, an expedient of forming the coil shape as a circular arc shape centered on the center of gravity of the bonding head has been proposed so as to reduce the offset between the direction of the driving force and the center of gravity. However, this results in more complicated structure. Furthermore, though a structure that accomplishes the connection between the Y direction actuator and the Y table by means of a joint connection instead of an arm can be used in order to reduce the size of the magnet, this causes a corresponding increase in the mass that must be driven. As a result, the size of the Y direction motor becomes larger in order to increase the Y direction driving force. Moreover, since a joint connection is used, a high rigidity cannot be obtained in these members. Furthermore, since the X table is moved, the center of the propulsion force of the Y direction actuator and the center of the load are offset, and it is difficult to increase the speed.